1. Field of the Invention
This invention generally relates to an exhaust system. This invention more particularly relates to an exhaust device to expel fumes from a kitchen.
2. Prior Art
Fumes including oil particles, smoke, odor and steam as well as harmful gaseous substances are unavoidably produced in a kitchen from cooking and imperfect combustion of cooking gas. Such fumes should be immediately expelled from the kitchen to keep the air in the kitchen always clean. Otherwise, the fumes will adversely affect not only people working in the kitchen but also the gas combustion of the cooking utensil. Such fumes will also stain the kitchen walls. Japanese Patent Laid-Open Publication No. 3-274325 discloses a ventilation fan that directly sucks and exhausts fumed kitchen air. It is also widely practiced to arrange a range hood over a gas table or range to directly suck up and exhaust fumes through an exhaust pipe or duct with the help of a blower.
Naturally, an exhaust system with a range hood can more effectively suck and evacuate fumed kitchen air than a ventilation fan or fans. For this reason, a range hood is often utilized for a so-called "system kitchen." It is true that the nearer a range hood is to a gas range, the more effective the exhaustion of fumed air from a kitchen will be.
However, the use of range hoods is not without a problem; there exists a major drawback in a conventional range hood system, i.e. unpleasant noise is generated during the operation of the system. This drawback is mainly due to the relatively limited dimension of an exhaust duct opening. A range hood is generally provided with a large opening to sufficiently cover a cooking range in order to collect most, if not all, fumed air directly therefrom, while an exhaust duct connected to the range hood is generally provided with a limited dimension which is much smaller than that of the range hood opening since exhaust ducts in general must be installed through walls and above ceilings. Exhaust ducts often have a dimension as small as 15 cm across. Exhaust ducts are also destined to be bent at a number of places on their way to the exit openings. Therefore, a powerful blower must be employed to forcibly expel fumes through such a narrow and bent duct, which will naturally generate much unpleasant noise. Noises are also generated when the fumed air running in an exhaust duct hits corner walls of the duct.
Any obstructive factor or element in the ventilation route of a range hood system not only deteriorates the expellant efficiency but also generates noises. Considering the fact that an exhaust duct is made much narrower than the opening of a range hood, through which fumes are expelled from a kitchen into the open air, there has been felt a demand for an exhaust device that can powerfully suck fumes into a range hood and into an exhaust duct to expel same into the open air with a much reduced noise level.
Some kitchens are furnished with a fresh air supply system in addition to an exhaust system to cooperatively provide an improved exhaustion of fumes. For such a kitchen, an exhaust system with a capacity "400 cubic meter/h" will sufficiently do the work to exhaust much of fumed air, however, an exhaust system with a capacity "500 cubic meter/h" or so will be required even with such a kitchen to also expel most of oil containing smoke from the kitchen. Without such a fresh air supply system, a kitchen will need an exhaust system having a capacity as powerful as "700 cubic meter/h, max." to exhaust substantially all fumed air containing oil particles and smoke. Such a powerful system does not match a small duct having a dimension of only about 15 cm across. If installed, such a powerful system will generate very unpleasant noise.
So-called "sirocco fans" may be employed in an appropriate way to reduce the noise level, however, a sirocco fan including its casing generally comes in a rather large overall dimension, demanding a substantial change in designing of the whole kitchen system including the design of its range hood, which is usually not feasible without major modification to the sirocco fan itself when the limited space of a kitchen is considered.
The inventor of the present invention has made efforts to find a way to effectively and substantially eliminate such noises from a kitchen exhaust system which incorporates a range hood, and has finally arrived at the present invention.